There are certain magical formula which operate throughout the centuries of Man's mental history in ever new ways. In Greece one such formula was regarded as an oracle of Apollo. It runs: "Know Thyself." Such sentences seem to conceal within them an unending life. One comes upon them when following the most diverse roads in mental life. The further one advances, the more one penetrates into the knowledge of things, the deeper appears the significance of these formula. In many a moment of our brooding and thinking, they flash out like lightning, illuminating our whole inner being. In such moments there quickens within us a feeling as if we heard the heart-beat of the evolution of mankind. How close do we not feel ourselves to personalities of the past, when the feeling comes over us, through one of their winged words, that they are revealing to us that they, too, had had such moments!